Question

In the present periodic table containing 118 elements:

How many elements belong to the third period?

Answer 1

STEP 1: The formula to find the number of elements in a period =

$\frac{{(n+2)}^2}{2}$: where ‘n’ is the period number, and ‘n’ is even.

$\frac{{(n+1)}^2}{2}$: where ‘n’ is the period number and ‘n’ is odd.

According to the question,

n = 3, and it is odd.

STEP 2: Applying the formula:

$\frac{{(3+1)}^2}{2}$

=$\frac{4^2}{2}$

=$\frac{16}{2}$

= $8$

Eight elements belong to the third period of a periodic table.